The five alien worlds most likely to support life

As scientists announce the discovery of a planet orbiting Alpha Centauri B, the closest star to our sun, it's just one of 750 planets found by space telescopes in recent years.

The new planet's surface is thought to be searingly hot and unlikely to support life - but scientists say that other worlds could orbit the same star.

But which worlds seen by our space telescopes are most likely to support life - or could it even lurk within our own solar system?

                             [Related: Earth-sized planet found orbiting our nearest star]

Name: Kepler 22b
Size: Earth
Location: Cygnus solar system
Distance from Earth: 620 light years
Could there be life?

Of all the candidate planets for possible life, Kepler 22b – nicknamed Earth 2.0 – has long been thought to be the most credible.

With an orbit of 290 days around a similar sun to our own, the average temperature is a balmy 22C – just 7C higher than on Earth.

Its Mediterranean-like climate means there could be water on the planet, which is 2.4 times the size of our own.

However, astronomers do not yet know for sure whether it has a predominantly gaseous, rocky or liquid composition.

Our best hope is that of a life-sustaining ocean.

 

Name: Gliese 667Cc
Size: Super-Earth
Location: Scorpius solar system
Distance from Earth: 22 light years
Could there be life?

Basking in the light of three suns, Gliese 667Cc has been dubbed Vulcan by astronomers after the triple-star system home to Star Trek’s Spock.

But, sci-fi asside, the reason scientists are most interested in the planet is that nestles nicely within the habitable zone of the red dwarf that it orbits.

It also absorbs as much energy from its star as we do from our Sun.

This offers the possibility of the existence of water, which is a prerequisite for life.

But, eight months after its discovery, atronomers are yet to find out what makes up the planet’s atmosphere.

 

Name: HD85512b
Size: Super-Earth
Location: Vela solar system
Distance from Earth: 36 light years
Could there be life?

The unromantic-sounding HD85512b, which so far has no common nickname, has a lot going for it – but not if you hate hot weather.

It neatly orbits an orange dwarf star at just the right distance for there to be water on its surface and for there to be a stable climate.

But its weather could be its big flaw. It has an average annual temperature of 25C – 10C higher than Earth.

It relies on 50 per cent cloud cover to avoid the mercury soaring above 50C.

Scientists are also trying to discover whether those clouds contain water – or potentially something possibly lethal.

Name: Kepler 47c
Size: Earth/Super-Earth/Gas giant
Location: Cygnus solar system
Distance from Earth: 5,000 light years
Could there be life?

Dubbed the New Tatooine – because, like the fictional planet in Star Wars, it has two suns – Kepler 47c augers some hope of finding aliens.

It resides in its parent star's habitable zone and that staralso has an intensity similar to that of our own Sun.

However, being a gas giant, Kepler 47c is not likely to be suitable for life as we know it.

But hope lies in the possibility that it might have moons – and, if found, these rocky outcrops could be an excellent bolthole for ET.

                      

Name: Mars
Size: Earth
Location: The Solar System
Distance from Earth: 140million miles
Could there be life?

The Red Planet has long been the subject of speculation over whether it could sustain life with illusory Martians a mainstay of science fiction.

However, beyond its relatively close proximity to Earth, it is also remarkably similar – hence why real scientists have been probing it for decades.

We know it contains many of the same minerals as our planet – including (frozen) water - and its days are roughly the same length.

Salty meltwater is also believed to lie only inches beneath the surface and the recent discovery of methane plumes in its  atmosphere points to potential life.

But the search for Martians is likely to continue for a long time yet.